Generally, ion implantation devices of this type are used to implant ions of a predetermined chemical species into semiconductor wafers in semiconductor manufacturing processes. Furthermore, such ion implantation devices include ion implantation devices with a so-called "mechanical scanning system" in which implantation is efficiently performed by a) positioning a multiple number of semiconductor wafers around the circumference of a rotation disk, b) causing said disk to rotate so that all of the semiconductor wafers are scanned at a high speed, and c) causing relative movement of the ion beam at a comparatively low speed in the radial direction of the rotating disk, so that the individual semiconductor wafers are scanned at a low speed.
Recently, in ion implantation devices, there has been a demand for an increase in the ion beam current in order to improve the productivity of semiconductor devices by shortening the ion implantation time. Hopes have been place in the above-mentioned ion implantation devices with mechanical scanning systems as ion implantation devices capable of handling such large-current ion beams.
However, in cases where a large-current ion beam is used, particles of impurities are created by sputtering which occurs as a result of parts other than the semiconductor wafers (e.g., the rotating disk) being irradiated by the ion beam. These impurity particles become mixed with the desired ions, and adhere to the semiconductor wafers, so that said semiconductor wafers become contaminated (below, this will be referred to as "contamination"). When impurity elements other than the desired ions thus become mixed with said ions and adhere to the wafers, the yield of semiconductor devices drops conspicuously.
Furthermore, it has also been indicated that in cases where the chemical species of ions being implanted is changed after certain ions have been implanted, contamination caused by the element previously being implanted (i.e., cross contamination) occurs.
Various methods have been proposed in order to prevent such contamination or cross contamination. For example, in Japanese Patent Application Kokai No. 61-116746, an ion implantation device is disclosed in which contamination caused by sputtering of the rotating disk is prevented by constructing a scanning arm assembly in which wafer attachment paddles are installed at equal intervals in a circular arrangement around a central hub, and wafers are attached to the tips of said paddles. This ion implantation device is constructed so that the scanning arm assembly is caused to rotate at high speed, and so that a cycloidal movement is performed at a low speed about the axis of the bottom part of the scanning arm assembly.
In such a construction, since wafer attachment paddles are installed as a disk, the portions of said paddles that are exposed to the ion beam can be reduced, so that the portions of the disk exposed to the ion beam can be greatly reduced; furthermore, as a result of the aforementioned cycloidal movement, the entire surface of each wafer can be irradiated with the ion beam.
However, in the above-mentioned ion implantation device using wafer attachment paddles, although the speed of the aforementioned cycloidal movement is controlled so that said speed is proportional to the distance from the axis of rotation, no consideration is given to fluctuations where there are changes in the ion beam current during the aforementioned low-speed cylocidal movement, the device cannot adequately respond to said changes; as a result, ions cannot be uniformly implanted.
One object of the present invention is to provide an ion implantation device a) which can reduce sputtering caused by exposure of the disk to the ion beam, and b) which can adequately respond to changes in the ion beam current during ion beam implantation.